This invention relates to directional valves and more particularly to a four-way, three-position poppet valve.
It is advantageous in many fluid control systems to have a directional valve structure having four selectable flow paths to control fluid flow from a pressure source to the apparatus being activated by the fluid. These "four-way" valves have heretofore been of several general types. The spool valve type generally includes a housing having an elongated bore with lateral inlet, outlet and exhaust ports communicating from the exterior of the housing to the bore area. A shaft is axially movable within the bore, and cylindrical enlargements or bosses on the shaft overlay various ports in different longitudinal positions to control the fluid flow from the inlet port to the outlet and exhaust ports and from the outlet ports to the exhaust ports. To prevent leakage between the shaft and the bore walls, these bosses are often provided with seals such as O-rings, which slidably engage the wall of the bore. These seals tend to wear rapidly as they must pass over the edges of the ports during the operation of the unit.
Another general type of four-way valve system includes a housing having an elongated bore therethrough with ports extending between the side wall of the housing. In contrast to the first type, this type of valve has valve seats extending radially inward from the walls of the bore between the ports, and the movable shaft within the bore is provided with poppet heads fixed on the shaft and arranged to engage selected valve seats as it is moved longitudinally within the bore. As the poppet heads move on a single shaft, to properly seal the fluid channels formed by the poppet heads against the valve seats, the seals of at least two poppet heads must engage two valve seats at the same time. Therefore, the two poppet heads must be exactly the same distance apart as their two respective valve seats. The required accuracy is so great that normal manufacturing tolerances are unacceptable, and the cost of making such valves is undesirably high. To overcome this difficulty, valves have been provided having movable valve seats in order to permit simultaneous sealing of poppet heads against valve seats as required. However, these valve systems require additional complex movable parts and additional seals which add to the cost and complexity of the unit.
Additionally, in this latter type of poppet valve structure, the prior art units have generally provided only two positions, that is fluid flow through two paths or fluid flow through the two alternative paths. Thus, in many of the prior art units, no center or neutral position, that is where all ports are either blocked or open, is provided.